JPH04336490A - Method for forming reflow solder - Google Patents

Abstract

PURPOSE:To enable soldering to be performed properly when joining a large-size parts electrode relatively for a land. CONSTITUTION:When coating a solder paste 8 for reflow using a screen mask 6 for a land 4 of a wiring pattern 4 on a printed-circuit board 2, the screen mask 6 with a larger area of an opening 6a than that of a land 4a is used and the solder paste 8 for reflow is coated over a wider area range than that of the land 4a and at the same time so that the land 4a is covered.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applied to lands of wiring patterns on a printed circuit board as a pre-process when assembling various electrical components such as IC chips, resistors, and capacitors to a printed circuit board by the solder reflow method. The present invention relates to a method of forming reflow solder (preliminary solder) by applying a reflow solder paste to the solder.

0002

2. Description of the Related Art FIGS. 3A and 3B show the steps of a conventional method for forming reflow solder of this type.

In FIG. 3A, 2 is a printed circuit board, 4 is a wiring pattern formed on the printed circuit board 2, and 4 is a printed circuit board.
a is a land formed as an end portion of the wiring pattern 4;

As shown in FIG. 3(b), a screen mask 6 having an opening 6a having the same shape and dimensions as the land 4a is attached to a printed circuit board with the opening 6a corresponding to the land 4a. 2 and apply reflow solder paste 8 onto the land 4a through the opening 6a.

FIG. 4 shows a state in which a small-sized electrical component 10 is electrically connected between a pair of lands 4a, 4a via reflowed solder paste 8a by the solder reflow method. 10a is an electrode, 10
b indicates the electrical component body.

In this case, one land 4a corresponds to each of the electrodes 10a on both sides, and since the size of each electrode 10a with respect to each land 4a is relatively small, reflow is not possible. The amount of solder paste 8a attached to the electrode 10a is sufficient, and soldering is performed well.

[0007]

However, as shown in the side view of FIG. 5(a) and the front view of FIG.
In order to electrically and mechanically bond the component electrode 12a, which has a relatively large size to the two lands 4a, with the reflowed solder paste 8a, the solder paste 8a
The amount of adhesion to the component electrode 12a was insufficient, which tended to cause poor soldering.

The reason for this is that when applying the reflow solder paste 8 using the screen mask 6, the opening 6a of the screen mask 6 always has the same area as the land 4a in both the case of FIG. 4 and the case of FIG. Therefore, the amount of reflow solder paste 8 applied to lands 4a having the same area was always the same.

The present invention was devised in view of the above circumstances, and it is possible to perform good soldering even if the component electrode to be bonded to the land is relatively large in size. The purpose of the present invention is to provide a method for forming reflow solder.

0010

[Means for Solving the Problems] A method for forming reflow solder according to the present invention is a method for forming reflow solder in which reflow solder paste is applied to lands of a wiring pattern on a printed circuit board using a screen mask. The area of the opening of the screen mask is made larger than the land, and the reflow solder paste is applied over an area wider than the land and covering the land.

[0011]

[Operation] When the solder paste is reflowed, the reflow solder paste that protrudes outside the outer periphery of the land is drawn in by the outer peripheral surface of the component electrode, and is integrated with the reflow solder paste on the land to form the bottom and outer peripheral surfaces of the component electrode. This will electrically and mechanically connect the surface of the land and the surface of the land.

[0012] When forming the reflow solder paste, the reflow solder paste was applied over an area wider than the land, so even if the size of the component electrode is relatively large compared to the land area, ,
A sufficient amount of solder paste adheres to the component electrodes, and soldering can be performed satisfactorily.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reflow solder forming method according to the present invention will be described in detail below with reference to the drawings.

FIGS. 1A to 1C show the steps of the reflow solder forming method according to this embodiment.

As shown in the perspective view of FIG. 1(a), a wiring pattern 4 is printed on the printed circuit board 2, and the ends of the wiring pattern 4 serve as lands 4a.

When applying reflow solder paste 8 to this land 4a using a screen mask 6 as shown in the cross-sectional view of FIG. 1(b), the area of the opening 6a is made larger than that of the land 4a. A screen mask 6 is used. A land 4 is located approximately in the center of the opening 6a.
The screen mask 6 is aligned so that point a is located, and the screen mask 6 is superimposed on the printed circuit board 2. Next, the reflow solder paste 8 is applied to the surface of the land 4a and the land 4a through the large opening 6a.
Coat the outer surface of the printed circuit board 2.

When the screen mask 6 is removed, as shown in the perspective view of FIG. 1(c), the reflow solder paste 8 has been applied to cover the land 4a over a wider area than the land 4a. Become.

Therefore, the amount of reflow solder paste 8 is sufficient when electrically and mechanically joining the component electrodes by the solder reflow method.

That is, the side view of FIG. 2(a) and (
As shown in the front view of b), a component electrode 12a having a relatively large size with respect to one land 4a is placed on the land 4a, and the reflow solder paste 8 is reflowed.

[0020] Then, the reflow solder paste 8a that had protruded outside the outer peripheral edge of the land 4a is drawn upward by the outer peripheral surface of the component electrode 12a, and
It becomes one with the reflow solder paste 8a on top. And this integrated reflow solder paste 8
a electrically and mechanically connects the bottom surface and outer peripheral surface of the component electrode 12a and the surface of the land 4a.

The total amount of the above-mentioned integrated reflow solder paste 8a corresponds to the outer circumferential length of the large-sized component electrode 12a, and the amount of the reflow solder paste 8a is sufficient for the component electrode 12a. Become something. Therefore, the mechanical bonding strength of the component electrode 12a to the land 4a is sufficient, making it possible to perform soldering well, improving the efficiency of soldering work, and at the same time increasing the reliability of soldering. be able to.

In the above embodiment, as shown in FIG. 1(c), the reflow solder paste 8 was applied with the longitudinal ends of the lands 4a exposed. Needless to say, the reflow solder paste 8 may be applied to cover the entire periphery and surface of the substrate.

[0023]

As described above, according to the present invention, the opening area of the screen mask is made larger than the land, and the reflow solder paste is applied over a wider area than the land. The reflow solder paste that protrudes from the periphery is also drawn in by the outer peripheral surface of the component electrode during reflow and becomes integrated with the reflow solder paste on the land, so the size of the component electrode is relatively large compared to the land area. too,
The amount of solder paste adhered to the component electrodes and the mechanical bonding strength can be made sufficient, and soldering can be performed satisfactorily.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the steps of a method for forming reflow solder according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state in which a large-sized component electrode is well soldered to a land in an example.

FIG. 3 is a diagram showing the steps of a conventional reflow solder forming method.

FIG. 4 is a diagram showing a state in which small-sized electrical components are connected across lands in a conventional example.

FIG. 5 is a diagram showing soldering defects when a large-sized component electrode is bonded to a land in a conventional example.

[Explanation of symbols]

2 Printed circuit board 4 Wiring pattern 4a Land 6 Screen mask 6a Opening 8 Reflow solder paste 8a Reflow solder paste 12a Component electrode

Claims (1)

[Claims] 1. A reflow solder forming method in which reflow solder paste is applied to lands of a wiring pattern on a printed circuit board using a screen mask, the area of the openings of the screen mask being larger than the lands. A method for forming reflow solder, which is characterized by applying reflow solder paste over an area wider than the land and covering the land.